dot methods completion

[xgdgsc]

Fixes #979 .

Updates #980.
completes

dframea = DataFrame()
dframea.

show list, then select append! to

append!(dframea,)

A few issues remain:

• cannot search the list
• the change in line 16 needed to show the list, I don' t know if it's right to change this.
• whether it' s ok to use dot as trigger.
• Some types don' t work, like Vector (Works in REPL runtime by Feat/methodswith dot completion julia-vscode#3240 )
• move cursor to middle of ",)"
• Would it be better to call methodswith in REPL mode?

I remember Golang does this in IDE. I think it' s a convenient way for people coming from OOP to find the relevant methods and gradually adapt to the Julian way. I' m looking for suggestions and opinions.